The present invention relates to laser devices, more particularly passively Q-switched laser devices, a method of generating controlled multiple lasing pulses with each illumination pulse of the laser flashlamp and a method of treatment using very high frequency lasing pulses.
Passively Q-switched laser devices have been known and used for several years. Such laser devices include a dye Q-switch, which is normally partially absorptive, aligned with its optical axis aligned with the laser rod and which serves as a gate, wherein the partial absorption bleaches when the lasing energy level reached a predetermined magnitude. Passively Q-switched laser devices have a substantial advantage over conventional multi-pulsed lasers, which require either that the laser be activated by applying a power in a repeated manner or by shuttering the laser output with a rapidly oscillating shutter, such as electro-optic switches, rotating mirrors or other active devices. A Q-switched laser device emits a series of identical lasing pulses which can be controlled in number from a single pulse to as many as 10 pulses.
Further, there are several types of commercially available lasers, including argon, ruby, carbon dioxide, krypton and neodymium doped glass end YAG laser rods. YAG lasers are preferred in certain medical applications because the YAG laser easily produces a short energy pulse with a high peak power. In medical applications, the laser rips electrons from the target atoms, leading to ionization of the tissue. YAG lasers have been utilized in the treatment of glaucoma, particularly after insertion of an artifical lens, wherein the lens becomes opaque, obscuring vision. The plasma created at the point of focus of the laser produces a shock wave which can be used to cut the opaque membrane at the back surface of the lens, within the vitreous fluid body of the eye, providing a noninvasive cutting procedure. Care, however, must be taken to focus the laser in such a manner to cut the opaque membrane and not damage the adjacent lens. The cutting plasma, generally described as a "microplasma", must therefore be of small size, approximately 50 microns, to limit the cutting to the desired area. The life of the plasma created by a single laser Q-switch pulse is approximately 20 to 200 microseconds at atmosphere pressure, such as found in the human eye. The size of the plasma and, therefore, the shock wave is determined by the energy of the laser pulse. Therefore, for a given Q-switch laser pulse, a given laser plasma size will result. In a conventional multi-pulsed laser, even a Q-switched laser, it is not possible to sustain the plasma created because the frequency of the pulses is greater than the life of the plasma created by a single laser pulse.
It is also desirable to increase the pulse repetition frequency of other multi-pulsed lasers, if the frequency can be increased without substantially increasing the energy required or the expense of the laser device. A more rapidly pulsing laser device would have many applications, including medical applications, such as opthomology, dermatology, microbiology and the like, and scientific applications, including ionization, spectrometry, spectryoscpy, etc. It is not possible, however, to substantially increase the frequency of conventional multi-pulsed lasers without substantially increasing the cost and reducing the reliability of the system. Finally, the cost and reliability of conventional laser systems have limited the applications for such lasers.
Many improvements have been made in lasers in recent years, including the development of athermal laser glass, the passively Q-switched lasers described above, and improvements in the laser components. It will be understood, however, that a laser is made up of several components which must be accurately aligned and which are easily damaged or misaligned. Further, laser systems remain relatively large and expensive. The need therefore remains for a more reliable, less expensive laser device, preferably a laser device wherein the components are permanently aligned and sealed. As described hereinbelow, the laser device of this invention permanently aligns the components of the laser system in a small package, which is more durable and less expensive than the laser devices of the prior art. Further, the laser device and method of this invention substantially increases the frequency of the pulses of the laser device, without increasing the expense or reducing the reliability of the system.